1. Field of the Invention
The present invention relates to a dye-sensitizer made of a novel heterocyclic tridentate ligand and dye-sensitized solar cells using the same.
2. Description of Related Art
Since Michael Grätzel proposed to fabricate a dye-sensitized solar cell (DSSC) by using a porous TiO2 thin film as a semiconductor electrode, and taking an organic metal compound as a photosensitive dye, together with a suitable redox electrolyte, this kind of solar cells has become one of the most promising third generation solar cells following silicon p-n junction solar cells. As the property of the dye for the dye-sensitized solar cell may directly affect the photoelectric conversion efficiency and commercial potentials of the solar cells, the photosensitive dye has become one of the key issues when researching this type of cells.
In the current development, a desirable photoactive dye is ML2(X)2, in which M represents ruthenium (Ru), L2 represents 4,4′-dicarboxyl-2,2′-bipyridine, and X represents halogen, cyano, thiocyanate, acetylacetonato, thiocarbamate, water, and the like. In this series of dyes, the “N3 dye”, in which X is thiocyanate, has the most desirable properties and with structure depicted below. However, as the matching degree between the absorption spectrum range for the N3 dyes and the solar spectrum is not desirable, and the N3 dye has a poor response to the spectrum of over 600 nm, so that this part of the solar energy cannot be effectively used.

Additionally, there is another photoactive dye called “black dye” [having a structural formula of RuL3(SCN)3(L=tripyridyltricarboxylate)], which can overcome the disadvantages of the N3 dye, and has a structure as follows.

Although the above two photoactive dyes have relatively high photoelectric conversion efficiency in the visible region and the “black dye” still has spectrum response at 920 nm, the “black dye” was not extensively employed as the photosensitive dye due to the tedious synthetic procedures and lower reaction yield.